ASN gives a level 2 rating on the INES scale to an incident which occurred during radiographic inspections leading to exposure of a worker from the SGS Qualitest Industrie company
On 18th April 2014, ASN was informed by the DCNS of an incident which occurred during the night of 17th to 18th April 2014 during radiographic inspections on the Nantes – Indret à La Montagne site (département 44). A team consisting of an operator from the OTECMI company’s Plabennec office (département 29), and an operator from the SGS Qualitest Industrie company’s Harfleur office (département 76), was carrying out radiographic inspections using a gamma ray projector containing a sealed radioactive source of iridium 192 with an activity of 1.95 TBq (terabecquerels) in one of the workshops on the DCNS site.
During a radiographic inspection, the radioactive source is ejected and guided through a tube to the exterior of the device opposite the parts to be inspected, behind which films are placed. The source is then located at a certain distance from the device. After the inspection, the source is returned to the device which constitutes a protective shield against the ionising radiation. These operations are performed by means of remote-control. A safety zone is set up around the device. When the radioactive source is in the protection position, the operator can approach the parts to be inspected in order to remove or position the films.
Believing the inspection to be completed, the operator of the SGS Qualitest Industrie company entered the safety zone to remove the film, even though the radioactive source was not in the protection position.
After being alerted by the radiographer from the OTECMI company, the operator from the SGS Qualitest Industrie company moved away from this zone. The two staff members then warned the persons with competence for radiation protection from their companies and the DCNS.
Owing to the limited duration of the exposure (about one minute), the dose received by the operator, recorded at 5.3 millisieverts (mSv) by his active dosimeter and at 2.85 mSv by his passive dosimeter, has no health consequences and is below the annual regulation dose limit of 20 mSv for a worker exposed during the course of his professional activity.
The ASN regional division of Nantes conducted an inspection on 15th May 2014. The inspection and the analysis of the event revealed that several essential radiation protection procedures had not been followed, more specifically with regard to zone entry instructions. The operator from the SGS Qualitest Industrie company approached the source in the irradiation position without using a radiation meter, despite the audible alarm on his active dosimeter being triggered and despite the signs specifically indicating that the source was in the irradiation position.
Owing to the failure to comply with all the rules concerning entry into the zone, which led to significant exposure of a worker, ASN rates this incident level 2 on the international INES scale, comprising 8 levels, from 0 to 7.